This invention relates to an extrusion and sizing process and more particularly to a new and improved method and apparatus for extruding and sizing thermo-plastic materials.
In the extrusion process of thermoplastic materials, reliance is made on the die means for shaping the product from the extruder. In certain instances the use of plastics for certain products has been hampered by the high temperatures necessary to economical manufacture of such products. One field that has some limitations is the vinyl house siding market. It is well-known to use rigid polymers for house siding and the like. Typical polymers for use are rigid polyvinyl chloride (PVC) as described in U.S. Pat. No. 3,890,268, chlorinated polyvinyl chloride (CPVC), and acrylonitrile-butadiene-styrene (ABS) polymers. Herein to process a compound that has good color retention other than white and pastels along with high impact resistance as well as good impact retention upon weathering, it is necessary to extrude the compound at a high enough temperature to take advantage of the excellent toughening effect of rubber impact modifiers which work best at temperatures above 380.degree. F. Processing siding made of PVC, CPVC or ABS at these temperatures is extremely difficult because the extrudate is too soft to handle and size properly. Accordingly, manufacturers producing the vinyl siding made of PVC, CPVC or ABS have limited their manufacturing to the fabrication of vinyl siding at a lower temperature range such as 350.degree. F. to 360.degree. F. to obtain a melt that is stiffer and more easy to size and handle. The present invention provides means and a process which permits extruding vinyl siding made of PVC, CPVC or ABS at high temperature such as above 380.degree. F. to permit the use of the excellent properties in weathering capstocks presently available to get excellent toughness. As an example of the capstock material used in siding such capstock can contain a vinyl chloride polymer, titanium dioxide and a plasticizer. See U.S. Pat. No. 4,100,325 for a further discussion on capstocks.
The present invention is directed to a process downstream of the extruder to provide a new and improved product. Accordingly, the description is directed to the process downstream of the extruder and not to the compound such as PVC, CPVC and ABS used in the process.